Technical Field
This disclosure relates to touch screen devices and to methods of operating touch screen devices. More particularly, the disclosure relates to touch screen devices which incorporate palm rejection in the presence of charger noise.
Discussion of the Related Art
A touch screen is a device that can detect an object in contact with or in proximity to a display area. The display area can be covered with a touch-sensitive matrix that can detect a user's touch by way of a finger or a stylus, for example. Touch screens are used in various applications such as mobile phones and other mobile devices. A touch screen may enable various types of user input, such as touch selection of items on the screen or alphanumeric input via a displayed virtual key pad. Touch screens can determine various parameters of the user's touch, such as the location, duration, etc.
One type of touch screen is a capacitive touch screen. A capacitive touch screen may include a matrix of conductive lines and columns overlaid on the display area. A change in capacitance between a line and a column may indicate that an object, such as a finger or a stylus, is touching the screen or is in proximity to the screen near the region of intersection of the line and column.
Some types of stylus have electronic functionality. In such cases, the touch screen device sends a wakeup signal at intervals during operation. If a stylus is within range and receives the wakeup signal, it responds with a synchronization signal. The synchronization signal is used to synchronize the stylus to the touch screen panel. During such use, any touching of the touch screen panel by the user's “palm” is rejected by the touch screen controller. As used herein, the term “palm” refers to any part of the user's hand, including but not limited to a finger, the palm or any other part of the hand.
It is commonplace that the touch screen device is used during the time when the device is plugged into a battery charger. Under such conditions, the touch screen device detects charger noise when the stylus or the palm contacts or is in proximity to the device. The charger noise degrades the ability of the touch screen device to detect the synchronization pulse from the stylus. Accordingly, there is a need for improved touch screen devices and methods for operating touch screen devices.